Periodontal disease is the major cause of tooth loss in adults. This disease is caused by bacteria, and one of the major goals of recent oral microbiology research has been the identification of the causative agents and the elucidation of their pathogenic mechanisms. Several candidate bacterial groups have been identified, and oral spirochetes presently are of great interest. Oral spirochetes are anaerobic, motile bacteria inhabiting the gingival crevice, where they are found in small numbers. In periodontal disease, these bacteria proliferate greatly and can account for as much as 50 percent of the microbial numbers in diseased sites. They are found at the advancing fronts of lesions, and have been associated with the most destructive forms of periodontal disease in which bone supporting the teeth is undergoing active destruction. The reasons for this distribution in diseased sites are not clear. Motile bacteria are chemotactic; i.e., they respond to chemical signals and move towards nutrients and away from irritants. Bacterial motility and chemotaxis have been invoked to explain the distribution of spirochetes in periodontal lesions, but no specific hypotheses have been tested. In this proposal it is planned to cultivate the oral spirochete Treponema denticola under strict anaerobiosis, and to determine growth conditions which produce highly motile bacteria. Preparations of motile bacteria will be tested for positive and negative chemotaxis to a variety of physiologically significant chemicals which might be found in periodontal pockets. These will include sugars, amino acids, vitamins, and fatty acids. Also, salts used in some types of periodontal therapy will be tested, as will the environmentally significant parameter, redox potential. These experiments will determine whether an oral spirochete can respond chemotactically under conditions which might be found in periodontal disease. Further experiments will probe the physiological regulation of chemotactic behavior in T. denticola.